1. Field of the Invention
The present invention relates to internal combustion engines and particularly to an intake manifold for multi-cylinder engines, an intake control unit utilizing the intake manifold and an intake manifold manufacturing method.
2. Description of Related Art
Utilizing the so-called intake inertia effect is an effective technique for improving performance in automotive internal combustion engines by increasing the air intake efficiency. However when the cross sectional area of the intake passage is fixed, the length of the intake passage at which maximum effect is delivered, becomes shorter as engine speed increases.
A method is publicly known in the conventional art in Japanese Laid Open Patent 60-216064 proposing cylindrical rotary valves operating according to engine speed and an intake control unit to distribute the required air for combustion in spiral intake passages in the same number of engine cylinders and enclosing the periphery of the rotary valves.
This intake control unit has a cylindrical casing mounted coaxially with the rotary valve at the periphery of the rotary valve. At the upper part of the casing, branch pipes equal in number to the engine cylinders are provided. These branch pipes are fixed on the cylinder head and connected with the intake port of the engine cylinder. As a result of this, an air intake system is constructed such as the air flows into each engine cylinder through the rotary valves and the spiral intake passages.
However, in the technology of the related art, the cylindrical casing provided on the periphery of the rotary valve and the plurality of branch pipes diverging from the casing were integrated with as a piece of intake manifold. Also, since each branch pipe provided a spiral intake passage enclosing the periphery of the rotary valve, core melting molding was utilized for producing the casing and the branch pipe into one piece. Especially, in order to achieve a light-weight of vehicle, it has been required that the above-mentioned parts are to be resinification.
However, the core melting molding needed for manufacturing the case and branch pipes (in other words, the intake manifold) had the drawback of requiring core production or troublesome melting processes after molding of the core. Therefore, it resulted in the disadvantage that the manufacturing process was not convenient.
In addition, another problem was that the intake inertia effect was unsatisfactory since air leaks occurred from the gap needed for rotary valve rotation.